By slowing and absorbing certain wavelengths of light, engineers open new possibilities in solar power, thermal energy recycling and stealth technology

“This advancement could prove invaluable for thin-film solar technology, as well as recycling waste thermal energy that is a byproduct of industry and everyday electronic devices such as smartphones and laptops.”

BUFFALO, N.Y. – More efficient photovoltaic cells.
Improved radar and stealth technology. A new way to recycle waste
heat generated by machines into energy.

All may be possible due to breakthrough photonics research at
the University at Buffalo.

The work, published March 28 in the journal Scientific Reports,
explores the use of a nanoscale microchip component called a
“multilayered waveguide taper array” that improves the
chip’s ability to trap and absorb light.

Unlike current chips, the waveguide tapers (the thimble-shaped
structures pictured above) slow and ultimately absorb each
frequency of light at different places vertically to catch a
“rainbow” of wavelengths, or broadband light.

“We previously predicted the multilayered waveguide tapers
would more efficiently absorb light, and now we’ve proved it
with these experiments,” says lead researcher Qiaoqiang Gan,
PhD, UB assistant professor of electrical engineering. “This
advancement could prove invaluable for thin-film solar technology,
as well as recycling waste thermal energy that is a byproduct of
industry and everyday electronic devices such as smartphones and
laptops.”

Each multilayered waveguide taper is made of ultrathin layers of
metal, semiconductors and/or insulators. The tapers absorb light in
metal dielectric layer pairs, the so-called hyperbolic
metamaterial. By adjusting the thickness of the layers and other
geometric parameters, the tapers can be tuned to different
frequencies including visible, near-infrared, mid-infrared,
terahertz and microwaves.

The structure could lead to advancements in an array of
fields.

For example, there is a relatively new field of advanced
computing research called on-chip optical communication. In this
field, there is a phenomenon known as crosstalk, in which an
optical signal transmitted on one waveguide channel creates an
undesired scattering or coupling effect on another waveguide
channel. The multilayered waveguide taper structure array could
potentially prevent this.

It could also improve thin-film photovoltaic cells, which are a
promising because they are less expensive and more flexible that
traditional solar cells. The drawback, however, is that they
don’t absorb as much light as traditional cells. Because the
multilayered waveguide taper structure array can efficiently absorb
the visible spectrum, as well as the infrared spectrum, it could
potentially boost the amount of energy that thin-film solar cells
generate.

The multilayered waveguide taper array could help recycle waste
heat generated by power plants and other industrial processes, as
well as electronic devices such as televisions, smartphones and
laptop computers.

“It could be useful as an ultra compact
thermal-absorption, collection and liberation device in the
mid-infrared spectrum,” says Dengxin Ji, a PhD student in
Gan’s lab and first author of the paper.

It could even be used as a stealth, or cloaking, material for
airplanes, ships and other vehicles to avoid radar, sonar, infrared
and other forms of detection. “The multilayered waveguide
tapers can be scaled up to tune the absorption band to a lower
frequency domain and absorb microwaves efficiently,” says
Haomin Song, another PhD student in Gan’s lab and the
paper’s second author.

Gan is a member of UB’s electrical engineering optics and
photonics research group, which includes professors Alexander N.
Cartwright (also UB vice president for research and economic
development), Edward Furlani and Pao-Lo Liu; associate professor
Natalia Litchinitser; and assistant professor Liang Feng.

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